Looks like you are tryning to visualize event in this way:
session.onpaymentauthorized = function (event) {
console.log(JSON.stringify(event))
}
this would shows only
{"isTrusted":true}
you can't stringify event:
https://stackoverflow.com/questions/11547672/how-to-stringify-event-object
try visualize payment responce from envent directly:
console.log(JSON.stringify(event.payment))